IGBT is a composite full-controlled type of voltage-driven power semiconductor device composed of BJT (Bipolar Junction Transistor) and MOSFET (Metal-Oxide-Semiconductor-Field-Effect-Transistor), which combines the high input impedance characteristics of MOSFETs with the low-saturation-voltage capability of BJT. The IGBT exhibits the features of high frequency, simple control circuit, high current density, and low on-state voltage, such that it is widely applied to the power control field. In the real practice, the IGBT is rarely used as an independent device, especially under conditions of inductive load, the IGBT requires a fast recovery diode freewheeling. Therefore, the conventional insulated gate bipolar transistor products usually employs a FWD (freewheeling diode) connected in parallel to protect the IGBT. In order to save the cost, the FWD can be integrated into the IGBT chip, thus forming the IGBT with a built-in diode or a reverse conducting IGBT.
In manufacturing a conventional reverse conducting IGBT, an implantation window of the back side of the P+ collector region is formed by double-sided photoetching after grinding. However, this method has two main drawbacks: first, a wafer grinding flow capacity is required, especially for those common IGBTs under 1200V which have a thickness less than 200 μm; second, a double-sided exposure machine is required to expose the wafer. In addition, the conventional reverse conducting IGBT is manufactured by a backside double photolithography technique.